Fermentation of the inoculated medium with Xanthomonas organisms for 36-72 hours under aerobic conditions, results in the formation of xanthan gum which is separated from other components of the medium by precipitation with acetone or methanol in a known manner. Because of the time required to ferment each batch, the low bipolymer content of the fermented medium and the processing steps required for the recovery and purification of the product, xanthan is relatively expensive.
Earlier work has indicated that the heteropolysaccharides produced by the action of Xanthomonas bacteria on carbohydrate media have potential application as film forming agents, as thickeners for body building agents in edible products, cosmetic preparations, pharmaceutical vehicles, oil field drilling fluids, fracturing liquids, and emulsifying, stabilizing, and sizing agents. Heteropolysaccharides, particularly xanthan gum, have significant potential as mobility control agents in micellar polymer flooding. Xanthan gum has excellent viscosifying properties at low concentration, it is resistant to shear degradation and exhibits only minimal losses in viscosity as a function of temperature, pH, and ionic strength. For these reasons, it is an attractive alternative synthetic polyacrylamides for enhanced oil recovery operations.
However, in order for xanthan gum to be used in enhanced oil recovery operations as a mobility control agent, the cost must be sufficiently low to make such operations economical. The economics of xanthan production by continuous fermentation are more favorable than when a batch fermentation process is employed. It has been shown that the economics of continuous xanthan fermentation are sensitive, at least in part, to the specific productivity at which the culture is operating. Therefore, any process improvements which enhance specific productivity will improve the overall economics. For example, at a dilution rate of 0.08 hr .sup.-1, increasing the specific productivity from 0.12 to 0.2 gm xanthan/gm cells/hr can lower the per pound price of xanthan by as much as 20%.
The most pertinent prior art of which I am aware is as follows:
1. P. Rogovin, et al., 1970, "Continuous Fermentation to Produce Xanthan Biopolymers: Laboratory Investigation", Biotechnol. Bioeng., XII, pp. 75-83.
2. K. W. Silman, et al., 1972, "Continuous Fermentation to Produce Xanthan Biopolymer: Effect of Dilution Rate", Biotechnol. Bioeng., XIV, pp. 23-31.
3. P. Rogovin, et al., U.S. 3,485,719, "Continuous Production of Xanthan".
4. G. P. Lindblom, et al., U.S. Pat. No. 3,328,262, "Heteropolysaccharide Fermentation Process".
5. Netherlands Patent Application No. 7,612,448, "Method for the Production of Bacterial Polysaccharides".
6. "Production of Polysaccharides by Xanthomonas campestris in Continuous Culture", FEMS Microbiology Letters, 347-349 (1978) by I. W. Davidson.
7. "Process for the Production of Xanthan Gum", British Patent Application No. 2,008,138 (A. Tate and Lyle, LTD).